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Multiplexing

Multiplexing

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Multiplexing

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  1. Multiplexing Prof. Choong Seon HONG

  2. 8 장 다중화(Multiplexing) 8.1 Many to One/One to Many 8.2 Type of Multiplexing 8.3 Multiplexing Application : Telephone system

  3. 다중화(Multiplexing) • 다중화(Multiplexing) • is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

  4. 다중화(Multiplexing) • Multiplexing vs. No Multiplexing

  5. 8.1 Many to One/One to Many • 다중화기(Multiplexer) • transmission streams combine into a single stream(many to one) • 역다중화기(Demultiplexer) • stream separates into its component transmission(one to many) and directs them to their intended receiving devices

  6. 8.2 Many to One/One to Many • Categories of Multiplexing

  7. FDM • FDM(Frequency-Division Multiplexing) • is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted

  8. FDM (cont’d) • FDM process • each telephone generates a signal of a similar frequency range • these signals are modulated onto different carrier frequencies(f1, f2, f3)

  9. FDM (cont’d) • FDM multiplexing process, time-domain

  10. FDM(cont’d) • FDM multiplexing process, frequency-domain

  11. FDM(cont’d) • Demultiplexing • separates the individual signals from their carries and passes them to the waiting receivers.

  12. FDM(cont’d) • FDM demultiplexing process, time-domain

  13. FDM(cont’d) • FDM demultiplexing, frequency-domain

  14. FDM(cont’d) • Example : Cable Television • coaxial cable has a bandwidth of approximately 500Mhz • individual television channel require about 6Mhz of bandwidth for transmission • can carry 83 channels theoretically

  15. 8.3 Wave Division Multiplexing (WDM) • WDM is conceptually same as FDM • except that the multiplexing and demultiplexing involve light signals transmitted through fiber-optic channels

  16. WDM (cont’d) • Combining and splitting of light sources are easily handled by a prism • Prism bends a beam of light based on the angle of incidence and the frequency.

  17. TDM(cont’d) • TDM(Time-Division Multiplexing) • is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving device

  18. TDM(cont’d) • TDM

  19. TDM(cont’d) • TDM can be implemented in two ways • Synchronous TDM • Asynchronous TDM

  20. TDM(cont’d) • Synchronous TDM • the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

  21. TDM(cont’d) • Frame • Time slots are grouped into frames • A frame consists of one complete cycle of time slots, including one or more slots dedicated to each sending device, plus framing bits.

  22. TDM(cont’d) • Synchronous TDM

  23. TDM(cont’d) • Interleaving • synchronous TDM can be compared to a very fast rotating switch • switch moves from device to device at a constant rate and in a fixed order 6 empty slots out of 24 are being wasted

  24. TDM(cont’d) • Demultiplexer decomposes each frame by discarding the framing bits and extracting each character in turn • Synchronous TDM, demultiplexing process

  25. TDM(cont’d) • Framing bits ~ allows the demultiplexer to synchronize with the incoming stream so that it can separate the time slots accurately (ex: 01010101 ….)

  26. TDM(cont’d) • Synchronous TDM Example 4 characters + 1 framing bit

  27. TDM(cont’d) • Asynchronous TDM : statistical time-division multiplexing Synchronous or Asynchronous : Not flexible or Flexible

  28. TDM(cont’d) • Examples of asynchronous TDM frames a. Case 1: Only three lines sending data

  29. TDM(cont’d) b. Case 2: Only four lines sending data

  30. TDM(cont’d) c. Case 3: All five lines sending data

  31. TDM(cont’d) • Inverse Multiplexing • takes the data stream from one high-speed line and breaks it into portion that can be sent across several lower speed lines simultaneously, with no loss in the collective data rate

  32. TDM(cont’d) • Multiplexing and inverse multiplexing

  33. TDM(cont’d) • Why do we need inverse multiplexing ? • wants to send data, voice, and video each of which requires a different data rate. [example] • voice - 64 Kbps link • data - 128 Kbps link • video - 1,544 Mbps link

  34. 8.5 Multiplexing application : Telephone system • Telephone Network

  35. Multiplexing application(cont’d) • Common Carrier Services

  36. Multiplexing application(cont’d) • Analog Service

  37. Multiplexing application(cont’d) • Analog Switched Service ~ is the familiar dial-up service most often encountered when using a home telephone (PSTN : Public Switched Telephone Network) • local loop : connection from the subscriber’s handset to the network

  38. Multiplexing application(cont’d) • Analog Leased Service : dedicated line ~ offers customers the opportunity to lease line(dedicated line), that is permanently connected to another customer. • No dialing is needed

  39. Multiplexing application(cont’d) • Analog Hierarchy • To maximize the efficiency of their infrastructure, telephone companies have traditionally multiplexed signals from lower bandwidth lines onto higher bandwidth lines.

  40. Multiplexing application(cont’d) • Analog hierarchy

  41. Multiplexing application(cont’d) • Digital Services • advantage - less sensitive than analog service to noise - lower cost

  42. Multiplexing application(cont’d) • Categories of digital service

  43. Multiplexing application(cont’d) • Switched/56 service ~ is the digital version of an analog switched line ~ allows data rates of up to 56Kbps

  44. Multiplexing application(cont’d) • DDS(Digital Data Service) ~ is the digital version of an analog leased line (maximum speed : 56Kbps)

  45. Multiplexing application(cont’d) • DS(Digital Signal) Service ~ is a hierarchy of digital signal

  46. Multiplexing application(cont’d) • DS Service • DS-0 : single digital channel of 64Kbps • DS-1 : 1,544Mbps, 24개의 64Kbps + 8Kbps의 overhead • DS-2 : 6,312Mbps, 96개의 64Kbps+168Kbps의 overhead • DS-3 : 44,376Mbps, 672개의 64Kbps+1.368Mbps의 overhead • DS-4 : 274,176Mbps,4032개의 64Kbps+16.128Mbps의 overhead

  47. Service Line Rate(Mbps) Voice Channels DS-1 DS-2 DS-3 DS-4 T-1 T-2 T-3 T-4 1,544 6,312 44,736 274,176 24 96 672 4032 Multiplexing application(cont’d) • T Lines

  48. Multiplexing application(cont’d) • T lines for Analog Transmission

  49. Multiplexing application(cont’d) • T-1 frame structure

  50. Multiplexing application(cont’d) • Fractional T Lines DSU/CSU (Data Service Unit / Channel Service Unit)